1. Field of Invention
The present invention relates to a method of fabricating a film. One of the major field of application of the film is in microelectronics in devices such as thin film transistors (TFTs) and metal insulator oxide (MOS) transistors.
2. Description of Related Art
A common way to deposit insulating, semiconducting and conducting films is employing a chemical vapor deposition (CVD) process. Three most commonly used CVD methods are: atmospheric pressure chemical vapor deposition (APCVD), low pressure chemical vapor deposition (LPCVD), and plasma enhanced chemical vapor deposition (PECVD).
During the CVD processes, the reactant gases are introduced in to a reaction chamber where they react at elevated temperature to form a film such as silicon dioxide film and silicon nitride film. During the CVD processes, parameters such as film deposition rate, deposition temperature and pressure are inter-related. Thus changing one parameter would affect other parameters. From the manufacturing-cost point of view, it is desired that the film should be deposited at low temperatures and as close as possible to the atmospheric pressure to reduce the high cost of vacuum tools. In the following, a quick overview is given of the order of temperatures (substrate temperature) and pressures used during depositions of silicon dioxide and silicon nitride depositions.
[Silicon dioxide deposition]
Silicon dioxide can be deposited at low temperature (300 to 500xc2x0 C.) by reacting silane, oxygen, and dopants (if needed) in a CVD reactor (APCVD) or at reduced pressure in an LPCVD reactor. The deposition rate decreases and the film properties degrade as the temperature is reduced, thus usually the deposition temperature is 450xc2x0 C. (or higher). These films are porous with lower density, lower dielectric strength, and higher etch rate in HF compared with the films produced using higher temperature process. The step coverage is also nonconformal.
The film properties can improved by increasing the deposition (substrate) temperature. For the deposition temperature range 500-800xc2x0 C., a silicon dioxide film can be formed by decomposing tetraethylorthosilicate, Si(OC2H5)4 or TEOS, in an LPCVD reactor, with improved film properties and conformal step coverage. At even higher temperature (900xc2x0 C.), silicon dioxide can be formed by reacting dichlorosilane, SiCl2H2, with nitrous oxide at reduced pressure.
Thus silicon dioxide films produced at higher deposition temperature have better properties, but applications can be limited, for example, these films can not be deposited over a layer of aluminum. Additionally, for TFT applications which use glass substrate, the deposition temperature need to be lower than 430xc2x0 C.
Alternatively, the films can be deposited by a PECVD process below 400xc2x0 C. However, this process requires the use of expensive vacuum tools as plasma processes are done at reduced pressures.
[Silicon Nitride Deposition]
Silicon nitride films can be deposited by an intermediate-temperature (750xc2x0 C.) LPCVD process or a low temperature (300xc2x0 C.) PECVD method. Although the films can be deposited at lower temperature using the PECVD method, the process would require the use of expensive vacuum equipment as was mentioned earlier.
Thus in the case of APCVD or LPCVD depositions of silicon dioxide and silicon nitride, the deposition temperature is too high to be useful for certain applications such as TFTs. Alternatively, the films can be deposited at lower temperatures using the plasma assisted process (PECVD), but the pressure in plasma assisted process is lower which requires expensive vacuum tools.
The object of the present invention is to at least provide an inexpensive and broad applicability method for fabricating insulating films such as silicon nitride and silicon oxide films, semiconducting or conducting films such as silicon films, and conducting films such as metal films at low temperatures. Semiconductor devices, which include the fabricated insulating, semiconducting or conducting films, can be used for electro-optical apparatuses, such as an LCD display and an electroluminescence display.
In accordance with one exemplary embodiment of the present invention, fabrication of insulating, semiconducting and conducting films by excitation of noble gases along with reactant gases at the pressures substantially close to atmospheric-pressure (about 100 kPa) is provided. This may completely eliminate the need of using vacuum tools, making the equipment and the process very inexpensive compared to equipment and processes used for making similar films in TFT and semiconductor industries.
The above exemplary embodiment of fabricating films at pressures substantially close to atmospheric-pressure may be advantageous from the cost and simplicity points of view. Accordingly, even if the process pressure is reduced to as low as 1 kPa, the processes can be carried out with inexpensive vacuum tools.